CN110282643A - A kind of modified oxidized aluminum material and its preparation method and application - Google Patents

Abstract

The embodiment of the invention discloses a kind of modified oxidized aluminum materials and its preparation method and application, this method comprises: sodium aluminate solution and rare earth nitrate solution spray are obtained mixed liquor into dispersant solution；Mixed liquor is subjected to precipitation process, aging process, is filtered, washed, presoma is obtained；Rare earth nitrate solution and ammonia spray into dispersion liquid and are carried out precipitation process, aging process, are filtered, washed, solid is obtained；Presoma and solid are dissolved in hot water respectively, and solid solution spraying into precursor solution and is stirred, end to be mixed carries out aging process, filtering, drying, washing, calcining, crushing, obtains modified oxidized aluminum material；The modified oxidized aluminum material that this method is prepared has excellent thermal stability, specific surface area and Kong Rong.

Description

A kind of modified alumina material and its preparation method and application

technical field

The embodiments of the present invention relate to the technical field of chemical materials, in particular to a modified alumina material and its preparation method and application.

Background technique

With the continuous development of society and the continuous progress of economy, automobiles have gradually become an indispensable means of transportation for people to travel. The number of cars owned by Chinese families and per capita continues to increase, and with the increase in the number of cars, a large amount of exhaust gas emitted into the air will bring more serious environmental problems and damage the city's climate and environment, such as a large amount of fog The formation of haze and acid rain, etc., and the harm of automobile exhaust to the atmospheric environment will also directly or indirectly cause harm to human health.

The three-way catalytic purification technology is a technology that installs a honeycomb ceramic filled with powder catalyst in the downstream of the engine to purify the exhaust gas generated by the engine. After gasoline is burned in the engine, it will mainly produce pollutants such as carbon monoxide, nitrogen oxides, hydrocarbons, and particulates. The exhaust gas passes through the three-way catalytic system, and the carbon monoxide, carbon oxides, and nitrogen oxides will be catalyzed by the catalyst. The reaction produces harmless substances such as water, carbon dioxide and nitrogen, among which the performance of the powder catalyst determines the purification ability of the three-way catalytic system.

Catalysts mainly include noble metal catalysts, catalytic promoters, stabilizers and γ-Al ₂ O ₃ coating materials, among which γ-Al ₂ O ₃ provides a larger surface area for the three-way catalyst, which ensures full contact between the catalyst and the exhaust gas, thus ensuring Catalytic efficiency; but when the temperature of γ-Al ₂ O ₃ reaches 800°C in a transient state, its structure transforms into α-Al ₂ O ₃ , and the specific surface area, pore volume, and oxygen storage and release capacity decrease, thereby reducing the catalytic efficiency. The position of the primary catalyst is close to the automobile engine, and its operating temperature can reach above 1000°C, so ordinary alumina cannot be used as the catalyst carrier in the three-way catalytic converter.

Contents of the invention

For this reason, the first purpose of the embodiment of the present invention is to provide a modified alumina material, which has excellent specific surface area and pore volume at a temperature higher than 800°C, and solves the problem of oxidation in the prior art. When the aluminum material is higher than 800°C, the specific surface area, pore volume, and oxygen storage and release capacity decrease.

The second purpose of the embodiments of the present invention is to provide a method for preparing a modified alumina material. The preparation method uses relatively simple equipment and is easy to operate, and uses various rare earth elements for modification, and high-temperature calcination treatment, so that the prepared Modified alumina materials have excellent thermal stability, specific surface area and pore volume.

The third purpose of the embodiment of the present invention is to provide an application of a modified alumina material in an automobile exhaust catalyst carrier. performance, which can effectively improve the durability and catalytic efficiency of the catalyst carrier.

In order to achieve the above purpose, embodiments of the present invention provide the following technical solutions:

According to the first aspect of the embodiments of the present invention, there is provided a method for preparing a modified alumina material, the preparation method comprising the following steps:

(a) spraying the sodium aluminate solution and the rare earth nitrate solution into the dispersant solution to obtain a mixed solution;

(b) subjecting the mixed solution to precipitation treatment, aging treatment, filtration and washing to obtain a precursor;

(c) spraying the rare earth nitrate solution and ammonia water into the dispersion liquid and performing precipitation treatment, aging treatment, filtering and washing to obtain a solid;

(d) Dissolving the precursor and the solid matter in hot water respectively, and spraying the solid matter solution into the precursor solution and stirring, after the stirring is completed, carry out aging treatment, filtration, drying, calcination, and pulverization to obtain the obtained The modified alumina material described above.

The above-mentioned preparation method of the present invention adopts relatively simple equipment, is easy to operate, and uses various rare earth elements for modification, and undergoes high-temperature calcination treatment, so that the prepared modified alumina material has excellent thermal stability, specific surface area and pore volume .

Further, in the step (a), the volume ratio of the sodium aluminate solution and the rare earth nitrate solution is 1: (0.8-1.2); the concentration of the sodium aluminate solution is 50-150g/L; the rare earth nitric acid in the rare earth nitrate solution The quality of the salt is 1-40% of the aluminum mass calculated as alumina in the sodium aluminate solution, and the solvent in the rare earth nitrate solution is a nitric acid solution with a mass fraction of 15-80%; the rare earth nitrate in the rare earth nitrate solution is selected from nitric acid Any two or more of lanthanum, cerium nitrate, zirconium nitrate, praseodymium nitrate, neodymium nitrate, barium nitrate and dysprosium nitrate. By limiting the concentration of the sodium aluminate solution, the particle size of the modified alumina material can be guaranteed, and the overall performance of the modified alumina material can be improved by the type and selection of rare earth nitrates.

Further, in the step (a), the volume ratio of the total volume of the sodium aluminate solution and the rare earth nitrate solution to the dispersant solution is 15: (2-3); the dispersant in the dispersant solution is selected from PEG-2000 , sodium dodecylbenzenesulfonate, polyvinylpyrrolidone, Tween 80, polyethylene glycol fatty acid ester and fatty acid polyoxyethylene ester; the quality of the dispersant in the dispersant solution is aluminum 0.1-10% of the mass of aluminum calculated as alumina in the sodium bicarbonate solution. Through the above definition, the specific surface area and pore volume of the prepared modified alumina material can be better improved.

Further, in the step (b), the precipitation treatment is to control the temperature of the mixed solution at 40-90° C. and the pH value to 6.5-8.5 under stirring conditions; the aging treatment is to age at 65-95° C. for 1-100 h. Through the above treatment, the high temperature thermal stability, specific surface area and pore volume of the prepared modified alumina material can be improved.

Further, in the step (c), the quality of the rare earth nitrate in the rare earth nitrate solution is 15-25% of the aluminum mass in the sodium aluminate solution, and the mass fraction of the solvent in the rare earth nitrate solution is 15% -80% nitric acid solution, the mass concentration of the rare earth nitrate solution is 250-350g/L, and the rare earth nitrate in the rare earth nitrate solution is selected from lanthanum nitrate, cerium nitrate, zirconium nitrate, praseodymium nitrate, neodymium nitrate, barium nitrate and nitric acid Any two or more of dysprosium; preferably, when the rare earth nitrate solution contains cerium nitrate, the cerium nitrate is first dissolved in the nitric acid solution, and hydrogen peroxide is added to the rare earth cerium nitrate solution and stirred well, wherein the hydrogen peroxide The mass concentration of hydrogen peroxide is 30%, and the amount of hydrogen peroxide added is 15-18% of the volume of the rare earth nitrate solution; the stirring time is 25-35min; Nitrate solution.

Further, in the step (c), the volume ratio of the rare earth nitrate solution, ammonia water and dispersion liquid is (5-7): (5-7): (4-6); the mass concentration of ammonia water is 45-55 %; the solute in the dispersion is selected from any one or more of PEG-2000, sodium dodecylbenzenesulfonate, polyvinylpyrrolidone, Tween 80, polyethylene glycol fatty acid ester and polyoxyethylene fatty acid ester species; the mass of the solute in the dispersion liquid is 4-6% of the mass of aluminum calculated as alumina in the sodium aluminate solution.

Further, in the step (c), the precipitation treatment is to adjust the pH value to 8.5-9.0 under stirring conditions; the aging treatment is to age at 70-80° C. for 20-26 hours.

Further, in the step (d), the stirring temperature is 75-85°C, and the stirring time is 3-5h; the aging treatment is aging at 70-80°C for 20-28h; the drying temperature is 85-95°C; The temperature is 800-1000°C, and the time is 2-10h; the pulverization is carried out by a ball mill to 25-35 μm; the temperature of the hot water is 85-95°C. The invention can improve the thermal stability of the prepared modified alumina material through calcining treatment.

Further, in the steps (b) and (c), the washing is to use distilled water to wash the filtrate, and add ammonia water during the washing process to adjust the pH to 8.0-10.0; the solid-liquid ratio of distilled water to the filtrate is (9-15 ): 1. The washing temperature is 60-95°C, the washing time is 10-60min, and the washing times are 3-5 times.

The invention can reduce the impurities in the prepared product through washing treatment, and can perform sodium removal, and can further improve the activity of preparing the modified alumina material.

According to the second aspect of the embodiments of the present invention, there is provided a modified alumina material prepared by the above preparation method.

The above-mentioned modified alumina material of the present invention has excellent thermal stability, specific surface area, pore volume and oxygen storage and release performance.

The third aspect of the embodiment of the present invention provides an application of the above-mentioned modified alumina material in a carrier of an automobile exhaust catalyst. By using the above-mentioned modified alumina material as a catalyst carrier, the service life of the catalyst carrier can be increased and the catalytic efficiency can be improved.

Embodiments of the present invention have the following advantages:

(1) The preparation method of the present invention adopts relatively simple equipment, is easy to operate, uses various rare earth elements for modification, and performs high-temperature calcination treatment to improve the comprehensive performance of the prepared product.

(2) The modified alumina material of the present invention has excellent thermal stability, specific surface area, pore volume and oxygen storage and release performance.

(3) The present invention can improve the service life of the catalyst carrier and improve the catalytic efficiency by using the modified alumina material as the catalyst carrier.

Detailed ways

The implementation mode of the present invention is illustrated by specific specific examples below, and those who are familiar with this technology can easily understand other advantages and effects of the present invention from the contents disclosed in this description. Obviously, the described embodiments are a part of the present invention. , but not all examples. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Example 1

This embodiment is a preparation method of a modified alumina material, and the preparation method includes the following steps:

(a) Spray the sodium aluminate solution and the rare earth nitrate solution with a concentration of 50g/L into the dispersant solution to obtain a mixed solution, wherein the volume ratio of the sodium aluminate solution and the rare earth nitrate solution is 1:0.8, and the aluminum acid The volume ratio of the total volume of the sodium solution and the rare earth nitrate solution to the dispersant solution is 15:2, the quality of the rare earth nitrate in the rare earth nitrate solution is 1% of the aluminum mass calculated as aluminum oxide in the sodium aluminate solution, and the rare earth nitric acid The solvent in the salt solution is a nitric acid solution with a mass fraction of 15%; the rare earth nitrate in the rare earth nitrate solution is lanthanum nitrate and dysprosium nitrate, and the dispersant in the dispersant solution is polyvinylpyrrolidone and Tween 80; the dispersant in the dispersant solution The mass is 0.1% of the mass of aluminum calculated as alumina in the sodium aluminate solution;

(b) Precipitate the mixed solution at 40°C, pH 6.5-8.5 and stirring conditions, then age at 95°C for 1 hour, filter, and then wash the filtrate with distilled water. During the washing process, add ammonia water to adjust the pH to 8.0, the solid-to-liquid ratio of distilled water to filtrate is 9:1, the washing temperature is 60°C, the washing time is 60min, and the washing times are 3 times to obtain the precursor;

(c) according to concentration is the rare earth nitrate solution of 350g/L, concentration is that the volume ratio of 45% ammonia water and dispersion liquid is 5:7:4, rare earth nitrate solution and ammonia water are sprayed in the dispersion liquid and at pH8. 5-9.0, carry out precipitation treatment under stirring conditions, then age at 70°C for 26 hours, then filter, and then use distilled water to wash the filtrate, add ammonia water during the washing process to adjust the pH to 8.0, the solid-liquid ratio of distilled water and filtrate is 9:1, the washing temperature is 60°C, the washing time is 60min, and the number of washings is 3 times to obtain a solid, wherein the solute in the dispersion is polyvinylpyrrolidone and Tween 80; the mass of the solute in the dispersion is alumina 4% of the aluminum mass in the sodium solution, the mass fraction of the rare earth nitrate in the rare earth nitrate solution is 15% of the aluminum mass in the sodium aluminate solution, and the mass fraction of the solvent in the rare earth nitrate solution is 15% % nitric acid solution, the rare earth nitrate in the rare earth nitrate solution is zirconium nitrate and praseodymium nitrate;

(d) Dissolve the precursor and solid matter in hot water at 95°C respectively, spray the solid matter solution into the precursor solution and stir at 75°C for 3h, and age at 80°C for 20h after the stirring is completed, Then filter and dry at 85°C, then calcined at 800°C for 10 hours, and pulverize to 25-35μm with a ball mill to obtain a modified alumina material.

Example 2

This embodiment is a preparation method of a modified alumina material, and the preparation method includes the following steps:

(a) Spray the sodium aluminate solution and the rare earth nitrate solution with a concentration of 150g/L into the dispersant solution to obtain a mixed solution, wherein the sodium aluminate solution and the rare earth nitrate solution are in a volume ratio of 1:1.2, and the aluminum The volume ratio of the total volume of the sodium aluminate solution and the rare earth nitrate solution to the dispersant solution is 5: 1, and the quality of the rare earth nitrate in the rare earth nitrate solution is 40% of the aluminum mass in the sodium aluminate solution calculated as aluminum oxide. The solvent in the nitrate solution is nitric acid solution with a mass fraction of 80%; the rare earth nitrate in the rare earth nitrate solution is selected from lanthanum nitrate, cerium nitrate and zirconium nitrate, and the dispersant in the dispersant solution is PEG-2000 and dodecylbenzene Sodium sulfonate; the quality of the dispersant in the dispersant solution is 10% of the aluminum quality calculated as aluminum oxide in the sodium aluminate solution;

(b) Precipitate the mixed solution at 90°C, pH6.5-8.5 and stirring conditions, then age at 65°C for 100h, filter, and then wash the filtrate with distilled water, add ammonia water during the washing process to adjust the pH to 10. The solid-to-liquid ratio of distilled water to filtrate is 15:1, the washing temperature is 95°C, the washing time is 10 min, and the washing times are 5 times to obtain the precursor;

(c) according to concentration is the rare earth nitrate solution of 250g/L, concentration is that the volume ratio of 55% ammonia water and dispersion liquid is 7:5:6, rare earth nitrate solution and ammonia water are sprayed in the dispersion liquid and at pH8. 5-9.0. Precipitate under stirring conditions, then age at 80°C for 20 hours, then filter, and then wash the filtrate with distilled water. During the washing process, add ammonia water to adjust the pH to 10. The solid-to-liquid ratio of distilled water and filtration is 15. : 1, the washing temperature is 95°C, the washing time is 10min, and the number of times of washing is 5 times to obtain a solid, wherein the solute in the dispersion is PEG-2000 and sodium dodecylbenzenesulfonate; The quality is 6% of the aluminum mass calculated as alumina in the sodium aluminate solution, the quality of the rare earth nitrate in the rare earth nitrate solution is 25% of the aluminum mass calculated as alumina in the sodium aluminate solution, and the solvent in the rare earth nitrate solution is A nitric acid solution with a mass fraction of 80%, and the rare earth nitrates in the rare earth nitrate solution are neodymium nitrate and barium nitrate;

(d) Dissolve the precursor and solid matter in hot water at 85°C respectively, spray the solid matter solution into the precursor solution and stir at 85°C for 5h, and age at 70°C for 28h after the stirring is completed, Then filter and dry at 95°C, then calcined at 1000°C for 2 hours, and pulverize to 25-35μm with a ball mill to obtain a modified alumina material.

Example 3

This embodiment is a preparation method of a modified alumina material, and the preparation method includes the following steps:

(a) Spray the sodium aluminate solution and the rare earth nitrate solution with a concentration of 100g/L into the dispersant solution to obtain a mixed solution, wherein the sodium aluminate solution and the rare earth nitrate solution are in a volume ratio of 1:1, and the aluminum The volume ratio of the total volume of the sodium aluminate solution and the rare earth nitrate solution to the dispersant solution is 6:1, and the quality of the rare earth nitrate in the rare earth nitrate solution is 3% of the aluminum mass in the sodium aluminate solution calculated as aluminum oxide. The solvent in the nitrate solution is a nitric acid solution with a mass fraction of 65%; the rare earth nitrate in the rare earth nitrate solution is praseodymium nitrate and neodymium nitrate, and the dispersant in the dispersant solution is PEG-2000 solution; the quality of the dispersant in the dispersant solution It is 5% of the mass of aluminum calculated as alumina in sodium aluminate solution;

(b) Precipitate the mixed solution at 80°C, pH7.0-7.5 and stirring conditions, then age at 90°C for 40h, filter, and then wash the filtrate with distilled water, add ammonia water during the washing process to adjust the pH to 9. The solid-to-liquid ratio of distilled water to filtration is 12:1, the washing temperature is 75°C, the washing time is 40 min, and the washing times are 4 times to obtain the precursor;

(c) Dissolve cerium nitrate in a nitric acid solution with a concentration of 65%, and add 30% hydrogen peroxide with a mass concentration of 30% in the rare earth cerium nitrate solution and stir for 30 minutes to mix evenly, then put the zirconium nitrate into the rare earth cerium nitrate solution to prepare The concentration of the rare earth nitrate solution is 300g/L, the quality of the rare earth nitrate in the rare earth nitrate solution is 18% of the aluminum mass calculated as aluminum oxide in the sodium aluminate solution, and the mass ratio of cerium nitrate and zirconium nitrate is 5:4 The amount of hydrogen peroxide added is 17% of the volume of the rare earth nitrate solution; subsequently, according to the volume ratio of the rare earth nitrate solution, the concentration of 50% ammonia water and the dispersion liquid is 6:6:5, the rare earth nitrate solution and ammonia water are sprayed Put it into the dispersion liquid and carry out precipitation treatment under the condition of pH 8.5-9.0 under stirring, then aging at 75°C for 24 hours, then filter, and then wash the filtrate with distilled water, add ammonia water during the washing process to adjust the pH to 9, distilled water The solid-liquid ratio with filtration is 12:1, the washing temperature is 75°C, the washing time is 40min, and the number of washings is 4 times to obtain a solid; the solute in the dispersion is PEG-2000; the mass of the solute in the dispersion is 5% of the mass of aluminum calculated as alumina in the sodium aluminate solution;

(d) Dissolve the precursor and solid matter in hot water at 90°C respectively, spray the solid matter solution into the precursor solution and stir at 80°C for 4 hours, and age at 75°C for 24 hours after the stirring is completed, Then filter, dry at 90°C, calcined at 900°C for 6 hours, and pulverize to 25-35μm with a ball mill to obtain a modified alumina material.

Comparative example 1

This comparative example is a preparation method of a modified alumina material, which is basically the same as the preparation method in Example 3, except that the rare earth nitrate solution in step (a) is a praseodymium nitrate solution; step (c) The medium rare earth nitrate solution is an aqueous solution of cerium nitrate.

Comparative example 2

This comparative example is a preparation method of a modified alumina material, the preparation method is basically the same as the preparation method in Example 3, the only difference is that the pH is not controlled during the precipitation treatment in step (b) and step (c) value.

Comparative example 3

This comparative example is a preparation method of a modified alumina material, which is basically the same as the preparation method in Example 3, except that no washing treatment is performed in step (b) and step (c).

Comparative example 4

This comparative example is the γ-Al ₂ O ₃ coating material used in the existing three-way catalytic system. The coating material is the coating material with the product number PURALOX SCFa-140L3 produced by Sasol manufacturer.

Experimental example 1

Select the modified alumina material prepared in the above-mentioned Examples 1-3 and Comparative Examples 1-4;

The surface area, pore volume, and content of γ-Al ₂ O ₃ of the above-mentioned materials in fresh state and after calcination at 900°C for 4 hours were detected by nitrogen adsorption method and transmission electron microscope respectively. The detection results are shown in Table 1:

Table 1

It can be seen from Table 1 that:

The rare earth composite modified alumina prepared in the embodiment of the present invention has excellent thermal stability, and can make the product have excellent specific surface area, pore volume and high γ-Al ₂ O ₃ content at 900°C; however, the control In the example, changing the preparation method of the present application and its raw materials has caused the reduction of the performance of the prepared product at high temperature, which affects the product performance; by comparing with the comparative example 4, the product prepared by the embodiment of the present invention has reached the product number of PURALOX SCFa -140L3 coating material comparable performance.

Although the present invention has been described in detail with general descriptions and specific examples above, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present invention. Therefore, the modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the protection scope of the present invention.

Claims (10)

1. a preparation method of modified alumina material, is characterized in that, comprises the steps: (a) spraying the sodium aluminate solution and the rare earth nitrate solution into the dispersant solution to obtain a mixed solution; (b) subjecting the mixed solution to precipitation treatment, aging treatment, filtration and washing to obtain a precursor; (c) spraying the rare earth nitrate solution and ammonia water into the dispersion liquid and performing precipitation treatment, aging treatment, filtering and washing to obtain a solid; (d) Dissolving the precursor and the solid matter in hot water respectively, and spraying the solid matter solution into the precursor solution and stirring, after the stirring is completed, carry out aging treatment, filtration, drying, calcination, and pulverization to obtain the obtained The modified alumina material described above. 2. preparation method according to claim 1, is characterized in that, in described step (a), sodium aluminate solution and rare earth nitrate solution volume ratio are 1: (0.8-1.2); Sodium aluminate solution concentration is 50-150g/L; the quality of the rare earth nitrate in the rare earth nitrate solution is 1-40% of the aluminum mass calculated as alumina in the sodium aluminate solution, and the solvent in the rare earth nitrate solution is nitric acid with a mass fraction of 15-80% Solution: The rare earth nitrate in the rare earth nitrate solution is selected from any two or more of lanthanum nitrate, cerium nitrate, zirconium nitrate, praseodymium nitrate, neodymium nitrate, barium nitrate and dysprosium nitrate. 3. preparation method according to claim 1, is characterized in that, in described step (a), the total volume of sodium aluminate solution and rare earth nitrate solution and the volume ratio of dispersant solution are 15: (2-3 ); in the dispersant solution, the dispersant is selected from any one or Various; the mass of the dispersant in the dispersant solution is 0.1-10% of the mass of aluminum calculated as alumina in the sodium aluminate solution. 4. The preparation method according to claim 1, characterized in that, in the step (b), the precipitation treatment is to control the temperature of the mixed solution to be 40-90° C. and the pH value to be 6.5-8.5 under stirring conditions; The treatment is aging at 65-95°C for 1-100h. 5. The preparation method according to claim 1, characterized in that, in the step (c), the quality of the rare earth nitrate in the rare earth nitrate solution is 15-25% of the aluminum quality calculated by alumina in the sodium aluminate solution. %, the solvent in the rare earth nitrate solution is a nitric acid solution with a mass fraction of 15-80%, the mass concentration of the rare earth nitrate solution is 250-350g/L, and the rare earth nitrate in the rare earth nitrate solution is selected from lanthanum nitrate, cerium nitrate, Any two or more of zirconium nitrate, praseodymium nitrate, neodymium nitrate, barium nitrate and dysprosium nitrate. 6. preparation method according to claim 1 is characterized in that, in described step (c), the volume ratio of rare earth nitrate solution, ammoniacal liquor and dispersion liquid is (5-7): (5-7): ( 4-6); the mass concentration of ammonia water is 45-55%; the solute in the dispersion is selected from PEG-2000, sodium dodecylbenzenesulfonate, polyvinylpyrrolidone, Tween 80, polyethylene glycol fatty acid ester and any one or more of fatty acid polyoxyethylene esters; the mass of the solute in the dispersion liquid is 4-6% of the mass of aluminum calculated as aluminum oxide in the sodium aluminate solution. 7. The preparation method according to claim 1, characterized in that, in the step (c), the precipitation treatment is to adjust the pH value to 8.5-9.0 under stirring conditions; the aging treatment is to age at 70-80°C 20-26h. 8. The preparation method according to claim 1, characterized in that, in the step (d), the stirring temperature is 75-85°C, and the stirring time is 3-5h; the aging treatment is aging at 70-80°C for 20 -28h; the drying temperature is 85-95°C; the calcination temperature is 800-1000°C, and the time is 2-10h; the pulverization is carried out by a ball mill to 25-35μm. 9. A modified alumina material, characterized in that it is prepared by the preparation method described in any one of claims 1-8. 10. The application of the modified alumina material as claimed in claim 9 in automobile exhaust catalyst carrier.